I didn't even noticed that we previously used 'provides'.  This should be removed and probably not encouraged.  That's because the semantics of this field is going to be changing in the next Python metadata version.  See for example: http://legacy.python.org/dev/peps/pep-0426/#id39  Same goes for 'requires' (which I believe has already been removed in another PR).

I think this is on the right track but still becoming increasingly complex, and also perhaps difficult to merge with the work for astropy_helpers.  But seeing this I'm leaning increasingly toward redoing all the setup stuff to just use d2to1, with whatever enhancements are needed there.  Toward that end maybe the actual python packages should just be listed in setup.cfg like:

```
[files]
packages = ...
```

which at this stage would seem a bit incongruous.  But if a d2to1-like setup is where we're headed it would be better to keep that in mind now so that fewer changes are needed later.